Powered screed and method of operating

ABSTRACT

A lightweight, powered screed machine for screeding the surface of a quantity of concrete having a pair of rails extending to either side, includes a frame having a handle arrangement, for manual engagement by an operator, and an elongated screed blade extending between the support rails. The machine further includes a powered vibration mechanism mounted on the frame. A pair of posts or masts are provided with one of the pair of posts attached to the frame adjacent each end of the blade and extending upward. Each of a pair of supports is positioned adjacent an associated end of the blade. Each support has rollers for engaging and riding on one of the pair of support rails, and each of the supports is attached to the frame so as to support the frame over the concrete. Each of the supports includes a linear actuator for raising and lowering the frame adjacent the rail. A pair of laser receivers is provided with each of the pair of laser receivers mounted on an associated one of the pair of posts. A control controls the linear actuators such that the screed blade is maintained at a desired height as the screed blade is moved over the concrete.

CROSS-REFERENCE TO RELATED APPLICATION

Not applicable.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

BACKGROUND OF THE INVENTION

This relates to a system for controlling the movement of a lightweight screed machine. More specifically, this relates to a system for controlling the vertical movement of a lightweight screed machine of the type that is manually moved generally horizontally over the surface of a quantity of concrete as the concrete cures to finish the surface at a desired height. The weight of the screed machine is supported on a pair of rails to some degree.

In concrete construction operations, after concrete is poured and spread, it is commonly finished by drawing a tool, called a screed, over the surface of the concrete. This process removes excess concrete and results in the top surface of the concrete being positioned at the proper elevation and grade. Numerous types of screeding devices have been used, both hand tools and powered tools of various sizes.

Hand screeding has commonly been accomplished with a manual screed device having a straight lower edge. This produces a flat upper surface on the concrete. The screed device is moved back and forth in a direction parallel to the screed edge in a sawing motion, while slowly advancing the screed across the concrete surface in a direction perpendicular to the screed edge. This is time consuming and labor intensive. Powered screed devices have been commonly used in construction for finishing larger areas of concrete, such as for example in finishing concrete slabs on highways, bridge decks, and deck slabs. Such screed devices may incorporate powered vibration mechanisms. Such mechanisms may include a rotated mass that has an off-center center of gravity. These mechanisms are commonly powered with electric motors or gasoline engines. Vibrating screed devices can finish relatively dry concrete more quickly, and are less fatiguing for operators, than are hand screed devices.

Lightweight powered screed devices typically include a vibration mechanism mounted on the frame of the screed machine, and a pair of handles that the screed operator uses to maneuver the screed manually over the surface of the concrete as the concrete is curing. Such lightweight powered screed devices are relatively easy to operate when smaller concrete areas, such as sidewalks and driveways, are being surfaced. Some skill is nevertheless required for the operator to achieve a smooth, uniform surface at the desired surface height, and the level of skill required increases with the size of the surface on which the screed device is to be used. It is common to provide a pair of screed support rails to either side of the concrete area being surfaced, and to support most of the weight of the screed device on these rails as the operator moves the screed machine along the curing concrete surface.

Larger screed machines have commonly used sophisticated automatic positioning controls to insure that that the larger expanses of concrete over which they operate are properly finished. Such machines are typically hydraulically powered, and the orientation and movement of the screed head is also controlled hydraulically. Typically, hydraulic cylinders connected to each end of the screed head raise and lower the ends independently. It has been common to determine the elevation of each end of the screed head by using a laser transmitter which provides a rotating beam of laser light, effectively producing a reference plane of laser light, and a pair of laser receivers. The laser receivers are mounted at each end of the screed head to detect the reference beam of laser light. The ends of the screed head are then raised or lowered hydraulically to produce the desired elevation for the concrete surface.

While large, hydraulically powered, screed machines have used sophisticated laser-based control arrangements to finish large areas of concrete surface at desired elevations, operating lightweight, powered screed devices has been largely accomplished without controls, and has remained a process that requires a certain amount of operator skill to achieve the best results.

SUMMARY OF THE INVENTION

A lightweight, powered screed machine for screeding the surface of a quantity of concrete having a pair of rails extending to either side, includes a frame having a handle arrangement, for manual engagement by an operator, and an elongated screed blade extending between the support rails. The machine further includes a powered vibration mechanism mounted on the frame. A pair of posts are provided with one of the pair of posts attached to the frame adjacent each end of the blade and extending upward. Each of a pair of supports is positioned adjacent an associated end of the blade. Each support has rollers for engaging and riding on one of the pair of support rails, and each of the supports is attached to the frame so as to support the frame over the concrete. Each of the supports includes a linear actuator for raising and lowering the frame adjacent the rail. A pair of laser receivers is provided, with each of the pair of laser receivers mounted on an associated one of the pair of posts. A control controls the linear actuators such that the screed blade is maintained at a desired height as the screed blade is moved over the concrete.

The machine may include a third mast, the third mast being adjacent to one of the pair of masts attached to the frame adjacent. A third support, positioned adjacent an associated end of the blade and one of the pair of supports, is configured to engage and ride on one of the pair of support rails. The third support is attached to one of the pair of supports, and includes an electric motor for changing the pitch angle of the screed as the third support is raised and lowered on the rail. A third laser receiver is mounted on the third mast. A third control circuit is also mounted on the third mast for controlling the electric motor of the third support such that the screed blade is maintained at a desired pitch as the blade is moved over the concrete.

The powered vibration mechanism may comprise a gasoline motor driving a rotating, off-center weight. The powered vibration mechanism may comprise an electric motor driving a rotating, off-center weight. The control for controlling the linear actuators such that the screed blade is maintained at a desired height as the screed blade is moved over the concrete may comprise a pair of control circuits, each control circuit controlling the linear actuator included in an associated one of the pair of supports. Each of the pair of control circuits may be mounted on an associated one of the pair of posts. A pair of displays may be provided with each of the pair of displays mounted on an associated one of the pair of supports. The displays are responsive to the control and to the laser receivers for providing a display of the operation of the screed machine. The linear actuator in each of the pair of supports may comprise an electric motor for raising and lowering the frame. Each of the pair of laser receivers may include an adjustable mount for attachment to an associated one of the pair of posts at a desired height for reception of a beam of laser light. The machine may further include a laser transmitter for projecting a reference beam of laser light to the pair of laser receivers.

A lightweight, powered screed machine for screeding the surface of a quantity of concrete having a pair of rails extending to either side, includes a frame having a handle arrangement, for manual engagement by an operator, and an elongated screed blade extending between the support rails. The machine further includes a powered vibration mechanism mounted on the frame. A pair of masts are provided with one of the pair of masts attached to the frame adjacent each end of the blade and extending upward. A pair of supports is provided with each of the pair of supports positioned adjacent an associated end of the blade. Each support is configured to engage and ride on one of the pair of support rails. Each of the supports is attached to the frame to support the frame over the concrete, and each of the supports includes an electric motor for raising and lowering the frame adjacent the rail. Each of a pair of laser receivers is mounted on an associated one of the pair of masts. Each of a pair of control circuits is also mounted on associated one of the pair of masts for controlling the electric motor of the support attached to the frame at the associated end of the blade. The screed blade is maintained at a desired height as it is moved over the concrete. A laser transmitter projects a reference beam of laser light for reception by the pair of laser receivers. The laser transmitter may project a substantially horizontal beam of laser light that rotates about a substantially vertical axis to define a generally horizontal reference plane of laser light.

The powered vibration mechanism may comprise a gasoline motor driving a rotating, off-center weight. The powered vibration mechanism may alternatively comprise an electric motor driving a rotating, off-center weight. Each of the pair of control circuits operates independently of the other of the pair of control circuits. Each of the pair of control circuits is mounted on an associated one of the pair of masts. The machine may further comprise a pair of displays, with each of the pair of displays mounted on an associated one of the pair of supports. The displays are responsive to the control circuit mounted on the associated mast, and to the laser receiver mounted on the associated mast, for providing a display of the operation of the screed machine. Each of the pair of laser receivers may include an adjustable mount for attachment to an associated one of the pair of masts at a desired height for reception of a beam of laser light.

A method of operating a powered screed of the type having a frame including a handle arrangement for manual engagement by an operator, and an elongated screed blade extending between the support rails, and a powered vibration mechanism mounted on the frame, and in which a pair of rails extends to either side a quantity of concrete, may comprising the steps of providing a pair of masts attached to the frame adjacent each end of the blade and extending upward; and providing a pair of supports at each end of the blade for riding on the support rails, with each support being attached to the frame and including a linear actuator for raising and lowering the frame and blade over the concrete. The method further includes the steps of providing a pair of laser receivers, each such receiver mounted on one of the pair of masts; projecting a beam of laser light for reception by the pair of laser receivers; and maintaining the screed blade at a desired height as the blade is moved manually over the surface of the concrete by operating the linear actuator in each of the pair of supports. The step of maintaining the screed blade at a desired height may include the step of operating the linear actuator to move the screed blade in dependence upon the relative height of the laser light which is received by the laser receivers. Further, the step of providing a pair of supports at each end of the blade for riding on the support rails, each support being attached to the frame and including a linear actuator for raising and lowering the frame and blade over the concrete may include the step of providing a pair of supports at each end of the blade for riding on the support rails. Each of the supports is attached to the frame and includes an electric motor for raising and lowering the frame and blade over the concrete.

A lightweight, powered screed machine for screeding the surface of a quantity of concrete having at least one rail adjacent the quantity of concrete, includes a frame having a handle arrangement for manual engagement by an operator, and an elongated screed blade extending between the support rails. A powered vibration mechanism is mounted on the frame. At least one post is attached to the frame adjacent an end of the blade and extends upward. At least one support is positioned adjacent an associated end of the blade. The support has rollers for engaging and riding on the at least one rail. The support is attached to the frame to support the frame over the concrete. The support includes a linear actuator for raising and lowering the frame adjacent the rail. At least one laser receiver is mounted on the at least one post. A control is provided for controlling the linear actuator such that the screed blade is maintained at a desired height as the screed blade is moved over the concrete. The control for controlling may include a control circuit. The control circuit may be mounted on the post, and the linear actuator may comprise an electric motor for raising and lowering the frame. A laser transmitter may be provided for projecting a reference beam of laser light to the laser receiver.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an embodiment of the lightweight, powered screed machine;

FIG. 2 is a schematic diagram of a control for the screed machine; and

FIG. 3 is a perspective view of a second embodiment of the lightweight, powered screed machine.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIGS. 1 and 2 illustrate an embodiment of the lightweight, powered screed machine 10. The machine 10 is positioned to smooth the surface of a quantity of concrete 12. A pair of rails 14 and 16 extend to either side of the concrete 12. The machine 10 has a frame 18 including a handle arrangement 19. The handle arrangement includes a pair of handles 20 and 22 that are grasped by the operator and used to pull the machine across the surface of the concrete 12. It will be appreciated, of course, that other types of handles may be used instead of the twin handles 20 and 22 that are shown. The handle arrangement is used by the operator to pull the machine generally to the right, as seen in FIG. 1. The frame 18 includes an elongated screed blade 24 that extends between the support rails 14 and 16, as well as channel members 19, and support elements 21 which extend between the screed blade 24 and the channel members 19 at each end of the screed blade 24.

The machine 10 includes a pair of posts or masts 26 and 28 that are attached to the frame 18, adjacent each end of the blade 18, and extend upward. A pair of supports 30 and 32 are provided adjacent the ends of the blade 24. Each support 30 and 32 includes a number of rollers 34 that engage and ride the support rails 14 and 16. Each of the supports 30 and 32 engages the channel members 19 of the frame 18 to support the frame 18 over the concrete 12. The supports 30 and 32 include linear actuators 36 for raising and lowering the frame 18 adjacent the rails upon which the supports ride. The linear actuators 36 may each comprise an electric motor 37 driving a threaded shaft 39 which raises and lowers an end of the frame 18. The channel members 19 each define threaded openings through which one of the threaded shafts 39 extends. Rotation of a threaded shaft 39 raises or lowers associated channel member 19. Channel members 19 also define openings which permit them to slide vertically on support posts 23.

A pair of laser receivers 38 and 40 are provided to sense illumination by a beam of laser light and to provide output signals indicating the relative positions of the beam striking the receivers. Each of the pair of laser receivers 38 and 40 is mounted on an associated one of the pair of masts 26 and 28 by an adjustable mount 42 and 44, respectively. The adjustable mounts 42 and 44 permit the heights of the receivers 38 and 40 to be altered so that the receivers are illuminated by a reference beam of laser light 46 from laser transmitter 48.

A control, comprising a pair of control circuits 50 and 52, controls the linear actuators 36 such that the screed blade 24 is maintained at a desired height as the screed blade 24 is moved over the concrete 12. Each control circuit controls the linear actuator 36 included in an associated one of the pair of supports 30 and 32. Control circuit 50 is responsive to laser receiver 38 to control the linear actuator 36 in support 30, while control circuit 52 is responsive to the laser receiver 40 to control the linear actuator 36 in support 32. Each of the pair of control circuits 50 and 52 is mounted on an associated one of the pair of posts or masts 26 and 28.

A powered vibration mechanism 54 is also mounted on the frame 18. The powered vibration mechanism 54 may include a gasoline motor driving a rotating, off-center weight arrangement. Alternatively, the powered vibration mechanism 54 may be an electric motor driving a rotating, off-center weight. The vibration mechanism vibrates the frame 18 and the screed blade 24, and facilitates the movement of the blade 24 over the surface of the curing concrete 12.

A pair of displays 56 and 58 are each mounted on an associated one of the pair of supports 26 and 28, respectively. The displays 56 and 58 are responsive to the controls 50 and 52, respectively, and to the laser receivers 38 and 40, respectively, for providing a display of the operation of the screed machine 10.

Laser transmitter 48 projects a reference beam of laser light 46 to the pair of laser receivers 38 and 40. The laser transmitter 48 projects a substantially horizontal beam 46 of laser light that rotates about a substantially vertical axis to define a generally horizontal reference plane of laser light. A horizontal reference plane may be used when screeding a horizontal surface on the concrete. If desired, however, the axis of rotation of the beam 46 can be slightly tilted by a specified pitch to produce a reference plane of laser light which is also slightly tilted. The tilted reference plane can be used to screed a concrete surface which is tilted at the same angle.

FIG. 2 illustrates the control circuit 50 in greater detail and shows the interconnections between the control circuit 50, the laser receiver 38, the display 56, and the motor 37. The control 50 includes a switch 60. When the end of the screed blade 24 is set at a desired position, the operator actuates switch 60 to store in memory 62 a signal then being received from laser receiver 38. The comparator 64 then compares the measured elevation from the laser receiver 38 with the stored elevation in the memory 62. When the comparator 64 determines that the measured and sensed elevations are no longer equal, the comparator 64 provides an output on 66 related to the difference in elevations to the motor drive circuit 68, which then drives motor 36 in the appropriate direction to reduce this difference. The display 56 receives both the signal from laser receiver 38 which indicates measured elevation and the signal on 66 which indicates the difference between the desired elevation and the measured elevation. The screed blade 24 is maintained at a desired height as the blade 24 is moved manually over the surface of the concrete 12 by operating the linear actuators 36 in the supports 30 and 32.

It will be appreciated that the control arrangement essentially provides separate control for each end of the screed blade which is unrelated to the elevation control for the other end of the screed blade. It will be appreciated, however, that if desired, the outputs from both of the laser receivers 38 and 40 may be used by a single control circuit to control both motors 37.

It will be appreciated that the control circuits 50, 52, motors 37, and displays 56, 58 all required electrical power. Further, in the instance in which the vibration 54 mechanism includes an electric motor, this requires electric power, as well. The power may be supplied from an external power source through power cables, or it may be provided by means of batteries carried on the screed machine 10. If the vibration mechanism includes a gasoline engine, the engine may be used to drive a small generator to produce the needed electric power.

Reference is made to FIG. 3, which illustrates a second embodiment of the lightweight, powered screed machine. Many of the elements of the screed machine shown in FIG. 3 are the same as those of the screed machine shown in FIG. 1, and they have therefore been designated with the same reference numerals. The screed machine of FIG. 3 provides for control of the pitch angle of the screed 24 as it is pulled across the surface of the concrete 12. To accomplish this, the screed machine includes a third mast 70. The third mast 70 is generally adjacent to one of the other masts 28 and is attached to the frame 18. The channel member 19′ extends between the support 30 and a third support 72 and attaches the two supports together. The third support 72 is positioned adjacent an associated end of the blade and one of the pair of supports 26. The third support is configured to engage and ride on the support rail 14. The third support 72 has the same type of linear actuator 36, including an electric motor 37, as the other supports 30 and 32. When the motor 37 is driven to raise or lower the support 72, the channel member 19′ is tilted, with the result that the pitch angle of the screed 24 is adjusted. A third laser receiver 74 is mounted on the third mast 70. A third control circuit 76 is mounted on the third mast 70 for controlling the electric motor 37 of the third support 72 such that the screed blade 24 is maintained at a desired pitch as the blade is moved over the concrete 12.

Although particular embodiments have been described above for purposes of illustration, it will be appreciated by those skilled in the art that numerous variations in these embodiments may be made. For example, the disclosed method may be used in conjunction with the operation of a drag box for laying asphalt or similar material. 

1. A lightweight, powered screed machine for screeding the surface of a quantity of concrete having a pair of rails extending to either side, comprising: a frame including a handle arrangement, for manual engagement by an operator, and an elongated screed blade extending between said support rails, a powered vibration mechanism mounted on said frame, a pair of posts, one of said pair of posts attached to said frame adjacent each end of said blade and extending upward, a pair of supports, each of said pair of supports positioned adjacent an associated end of said blade, each support having rollers for engaging and riding on one of said pair of support rails, each of said supports attached to said frame so as to support said frame over said concrete, each of said supports including a linear actuator for raising and lowering said frame adjacent said rail, a pair of laser receivers, each of said pair of laser receivers mounted on an associated one of said pair of posts, and a control for controlling said linear actuators such that said screed blade is maintained at a desired height as said screed blade is moved over said concrete.
 2. A lightweight, powered screed machine for screeding the surface of a quantity of concrete according to claim 1, in which said powered vibration mechanism comprises a gasoline motor driving a rotating, off-center weight.
 3. A lightweight, powered screed machine for screeding the surface of a quantity of concrete according to claim 1, in which said powered vibration mechanism comprises an electric motor driving a rotating, off-center weight.
 4. A lightweight, powered screed machine for screeding the surface of a quantity of concrete according to claim 1, in which said control for controlling said linear actuators such that said screed blade is maintained at a desired height as said screed blade is moved over said concrete comprises a pair of control circuits, each control circuit controlling the linear actuator included in an associated one of said pair of supports.
 5. A lightweight, powered screed machine for screeding the surface of a quantity of concrete according to claim 4, in which each of said pair of control circuits is mounted on an associated one of said pair of posts.
 6. A lightweight, powered screed machine for screeding the surface of a quantity of concrete according to claim 1, further comprising a pair of displays, each of said pair of displays mounted on an associated one of said pair of supports, said displays being responsive to said control and to said laser receivers for providing a display of the operation of the screed machine.
 7. A lightweight, powered screed machine for screeding the surface of a quantity of concrete according to claim 1, in which said linear actuator in each of said pair of supports comprises an electric motor for raising and lowering said frame.
 8. A lightweight, powered screed machine for screeding the surface of a quantity of concrete according to claim 1, in which each of said pair of laser receivers includes an adjustable mount for attachment to an associated one of said pair of posts at a desired height for reception of a beam of laser light.
 9. A lightweight, powered screed machine for screeding the surface of a quantity of concrete according to claim 1, further comprising a laser transmitter for projecting a reference beam of laser light to said pair of laser receivers.
 10. A lightweight, powered screed machine for screeding the surface of a quantity of concrete having a pair of rails extending to either side, comprising: a frame including a handle arrangement, for manual engagement by an operator, and an elongated screed blade extending between said support rails, a powered vibration mechanism mounted on said frame, a pair of masts, one of said pair of masts attached to said frame adjacent each end of said blade and extending upward, a pair of supports, each of said pair of supports positioned adjacent an associated end of said blade, each support configured to engage and ride on one of said pair of support rails, each of said supports attached to said frame so as to support said frame over said concrete, each of said supports including an electric motor for raising and lowering said frame adjacent said rail, a pair of laser receivers, each of said pair of laser receivers mounted on an associated one of said pair of masts, a pair of control circuits, one of said pair of control circuits mounted on each of said pair of masts, for controlling said electric motor of the support attached to the frame at the associated end of said blade, such that said screed blade is maintained at a desired height as said screed blade is moved over said concrete, and a laser transmitter for projecting a reference beam of laser light for reception by said pair of laser receivers.
 11. The lightweight, powered screed machine of claim 10, in which said laser transmitter projects a substantially horizontal beam of laser light that rotates about a substantially vertical axis to define a generally horizontal reference plane of laser light.
 12. The lightweight, powered screed machine of claim 10, in which said powered vibration mechanism comprises a gasoline motor driving a rotating, off-center weight.
 13. The lightweight, powered screed machine of claim 10, in which said powered vibration mechanism comprises an electric motor driving a rotating, off-center weight.
 14. The lightweight, powered screed machine of claim 10, in which each of said pair of control circuits operates independently of the other of said pair of control circuits.
 15. The lightweight, powered screed machine of claim 14, in which each of said pair of control circuits is mounted on an associated one of said pair of masts.
 16. The lightweight, powered screed machine of claim 10, further comprising a pair of displays, each of said pair of displays mounted on an associated one of said pair of supports, said displays being responsive to the control circuit mounted on the associated mast and to the laser receiver mounted on the associated mast for providing a display of the operation of the screed machine.
 17. The lightweight, powered screed machine of claim 10, in which each of said pair of laser receivers includes an adjustable mount for attachment to an associated one of said pair of masts at a desired height for reception of a beam of laser light.
 18. A method of operating a powered screed of the type having a frame including a handle arrangement for manual engagement by an operator, and an elongated screed blade extending between said support rails, and a powered vibration mechanism mounted on said frame, and in which a pair of rails extends to either side a quantity of concrete, comprising the steps of: providing a pair of masts attached to the frame adjacent each end of the blade and extending upward, providing a pair of supports at each end of the blade for riding on the support rails, each support attached to the frame and including a linear actuator for raising and lowering the frame and blade over the concrete, providing a pair of laser receivers, each such receiver mounted on one of the pair of masts, projecting a beam of laser light for reception by said pair of laser receivers, maintaining said screed blade at a desired height as said blade is moved manually over the surface of the concrete by operating said linear actuator in each of said pair of supports.
 19. The method of claim 18 in which said step of maintaining said screed blade at a desired height includes the step of operating said linear actuator to move said screed blade in dependence upon the relative height of the laser light which is received by said laser receivers.
 20. The method of claim 18 in which said step of providing a pair of supports at each end of the blade for riding on the support rails, each support attached to the frame and including a linear actuator for raising and lowering the frame and blade over the concrete includes the step of providing a pair of supports at each end of the blade for riding on the support rails, each support attached to the frame and including an electric motor for raising and lowering the frame and blade over the concrete.
 21. A lightweight, powered screed machine for screeding the surface of a quantity of concrete having at least one rail adjacent the quantity of concrete, comprising: a frame including a handle arrangement, for manual engagement by an operator, and an elongated screed blade extending between said support rails, a powered vibration mechanism mounted on said frame, at least one post attached to said frame adjacent an end of said blade and extending upward, at least one support positioned adjacent an associated end of said blade, said support having rollers for engaging and riding on said at least one rail, said support attached to said frame so as to support said frame over said concrete, said support including a linear actuator for raising and lowering said frame adjacent said rail, at least one laser receiver, said laser receiver mounted on said at least one post, and a control for controlling said linear actuator such that said screed blade is maintained at a desired height as said screed blade is moved over said concrete.
 22. A lightweight, powered screed machine for screeding the surface of a quantity of concrete according to claim 21, in which said control for controlling said linear actuator such that said screed blade is maintained at a desired height as said screed blade is moved over said concrete comprises a control circuit, said control circuit controlling said linear actuator included said support.
 23. A lightweight, powered screed machine for screeding the surface of a quantity of concrete according to claim 22, in which said control circuit is mounted on said post.
 24. A lightweight, powered screed machine for screeding the surface of a quantity of concrete according to claim 21, in which said linear actuator comprises an electric motor for raising and lowering said frame.
 25. A lightweight, powered screed machine for screeding the surface of a quantity of concrete according to claim 21, further comprising a laser transmitter for projecting a reference beam of laser light to said laser receiver.
 26. A lightweight, powered screed machine for screeding the surface of a quantity of concrete having a pair of rails extending to either side, comprising: a frame including a handle arrangement, for manual engagement by an operator, and an elongated screed blade extending between said support rails, a powered vibration mechanism mounted on said frame, a pair of masts, one of said pair of masts attached to said frame adjacent each end of said blade and extending upward, a pair of supports, each of said pair of supports positioned adjacent an associated end of said blade, each support configured to engage and ride on one of said pair of support rails, each of said supports attached to said frame so as to support said frame over said concrete, each of said supports including an electric motor for raising and lowering said frame adjacent said rail, a pair of laser receivers, each of said pair of laser receivers mounted on an associated one of said pair of masts, a pair of control circuits, one of said pair of control circuits mounted on each of said pair of masts, for controlling said electric motor of the support attached to the frame at the associated end of said blade, such that said screed blade is maintained at a desired height as said screed blade is moved over said concrete, a laser transmitter for projecting a reference beam of laser light for reception by said pair of laser receivers, a third mast, said third mast being adjacent to one of said pair of masts attached to said frame, a third support, positioned adjacent an associated end of said blade and one of said pair of supports, said third support configured to engage and ride on one of said pair of support rails, said third support attached to said one of said pair of supports, said third support including an electric motor for changing the pitch angle of the screed as said third support is raised and lowered on said rail, a third laser receiver mounted on said third mast, and a third control circuit mounted on said third mast for controlling said electric motor of the third support such that said screed blade is maintained at a desired pitch as the blade is moved over said concrete.
 27. The lightweight, powered screed machine of claim 26, in which said laser transmitter projects a substantially horizontal beam of laser light that rotates about a substantially vertical axis to define a generally horizontal reference plane of laser light. 